High‐performance Liquid Chromatography/Atmospheric Pressure Chemical Ionization Mass Spectrometry with Ionization Polarity Switching for the Determination of Selected Pesticides

A high performance liquid chromatographic/atmospheric pressure chemical ionization mass spectrometric (APCI-MS) method has been developed for the determination of 10 pesticides. Initial comparison was made between the two atmospheric pressure ionization techniques, APCI and electrospray. Optimum separation of the compounds was obtained using a Hypersil carbamate column with a 0.05M ammonium acetate/acetonitrile isocratic elution at a flow rate of 0.5 mL/min. A positive/negative ionization mode switch was operated during each acquisition enabling the determination of 8 of the compounds in the positive ionization mode and 2 of the compounds in the negative ionization mode. The method was applied to the determination of all 10 compounds in extracts of strawberries and plums. Limits of detection were both compound and matrix dependent and ranged from 0.002–0.025 ng/μL in solvent-based standards and 0.003–0.05 ng/μL in matrix-matched standards (equivalent to 0.002–0.033 mg/kg in the crop). Where set, current Codex Alimentarius Commission and UK Maximum Residue Levels are clearly met by the sensitivity achieved by this method. © 1997 Crown Copyright